Environmentalists and politicians in Australia are upset over news that the U.S. Navy dropped four unarmed bombs onto the endangered Great Barrier Reef during a joint military training exercise.

U.S. Navy officials said the ordnance were dumped on July 16 by two AV-8B Harrier aircraft after they ran out of fuel and were forced to take emergency measures. A pre-arranged drop zone was not used due to the presence of civilian vessels, which had strayed into area without authorization.

Naval commanders insisted the unexploded weapons—which weighed a total of 1.8 tons and included two unarmed laser-guided bombs and two inert practice bombs—were not a danger to the reef’s fragile ecosystem.

But members of environmental organizations and the Australian government demanded answers about the incident, and for the U.S. to remove the bombs.

“We need to know why it happened,” World Wildlife Fund-Australia's Richard Leck told National Geographic. “There’s an enormous amount of threats around the reef...and having more threats occur in this form is certainly the last thing the reef needs.”

Felicity Wishart of the Australian Marine Conservation Society said she wants the U.S. and Australia to stop conducting exercises near the reef. The biennial event lasts three weeks and has the participation of 28,000 U.S. and Australian military personnel.

Australian Senator Larissa Waters called the bomb droppings “outrageous.”

“Have we gone completely mad?” Waters told the Australian Broadcasting Corp. “Is this how we look after our World Heritage area now? Letting a foreign power drop bombs on it?”

Lieutenant David Levy, a spokesman for the U.S. 7th Fleet, said the Navy was currently reviewing the possibility of retrieving the bombs.

Stretching across 1,800 miles of Australia’s northeast coast, the Great Barrier Reef is Earth’s largest single structure built by living organisms. It has, in recent years, come under assault from the damaging effects of climate change and the ongoing dumping of toxic industrial waste.

The naval exercise bomb incident comes only months after another U.S. Navy mishap in the Pacific near the Philippines. On January 17, the USS Guardian ran aground on Tubbataha Reef in the Sulu Sea. A naval investigation characterized the event as a “tragic mishap.”

Admiral Cecil D. Haney, commander of the U.S. Pacific Fleet, wrote in the 160-page report that “USS Guardian leadership and watch teams failed to adhere to prudent, safe, and sound navigation principles which would have alerted them to approaching dangers with sufficient time to take mitigating action.”

Haney blamed a “lack of leadership” for the team’s failure to take into account visual and electronic cues leading up to the grounding, resulting in a reliance on inaccurate digital nautical charts.